It is known that the combustion reaction between fuel and comburent in gas burners is achieved by means of a combustion head that substantially comprises a tubular duct, which conveys the comburent fluid originating from a blower to the combustion chamber where it mixes with a gaseous fuel delivered by means of one or more nozzles.
An ignition device of known type sparks off the mixture, thereby starting the combustion.
Likewise, it is known that one of the main problems with combustion heads, from the environmental-impact viewpoint, consists in that they produce nitric oxides NOx during combustion, which cause pollution.
Study of the phenomena of producing nitric oxides NOx has shown that they are chiefly generated when the flame temperature is high. In fact, it has been experimentally observed that NOx production increases in a substantial manner when the flame is around 1200-1400° C.
For this reason, burners have been developed with combustion heads in which reduction of flame temperature takes place by recirculating part of the smoke produced during combustion inside the combustion head where the flame is present.
In fact, the smoke present in the combustion chamber is attracted to the flame and, as it does not take part in the combustion reaction, it absorbs heat, cooling the flame and thereby reducing nitric oxide NOx emissions.